In electrolytic refining or electrowinning, which is used as a sub-process in the production of metals, such as copper, nickel and zinc, the cathode electrode employed at present is commonly a mother plate made of stainless steel, and the metal to be refined is precipitated on both sides of said mother plate. If the mother plate edges are not protected with an edge strip made of some insulating material, the deposits created in the refining or electrowinning process on both sides of the mother plate will grow together. Such edge strips and their use is described for example in the EP patent application 454,056 and in the FI patent application 955,919.
The edge strips used in the mother plate are generally installed on the mother plate surface, in which case the surface-installed edge strips are susceptible to damage when the deposits are being removed. Particularly the bottom edge strip, located on the opposite side with respect to the fastening edge of the hanger bar of the mother plate, is prone to damage, because the deposits are usually removed from the hanger bar direction towards the bottom edge strip. Although the bottom edge strip were not damaged during deposit removal, the edge strip installed on the mother plate surface gathers impurities that weaken the purity of the deposit created on the mother plate surface.
In order to obviate the drawbacks caused by edge strips installed on the mother plate surface, the FI patent application 863,244 introduces an edge strip which is installed in a dovetail groove, so that part of the edge strip is placed in said groove in order to support the external part of said groove.
The edge strip is formed of a polymer film, folded in its longitudinal direction; a stainless steel wire is placed in the fold, and the overlapping film halves, located on top of each other, are joined in a watertight fashion. The edge strip formed in said fashion is drawn in, together with the included wire, starting from the bottom end of the grooved cathode edge. Thus the edge strip is drawn over the topmost horizontal cathode edge, so that the overlapping part facilitates the replacing of a used edge strip at some later stage. By means of the stainless steel wire placed in the groove, the edge strip is protected from being protruded or drawn out of the wedge-shaped aperture during usage. However, the edge strip according to the FI patent application 863,244 is not suited to be realized as a uniform strip covering all three edges of the cathode plate, because the problems caused by the bottom corners of the cathode plate, left in between the vertical edge strips and the horizontal edge strip, are equally serious as with traditional external edge strips. Moreover, the structure of the edge strip is not necessarily suitable for ordinary cathode plate thicknesses, because for instance the use of stainless steel wire requires a given addition in the cathode plate thickness.